i am writing this opinion as a webtoon reader of the original... and i honestly would have preferred if this was readapted into a mini-series instead of a movie.. and here's why i felt so..

STORY
I may be biased since I am comparing it to the webtoon, but honestly if this was a drama, there would have been more time to understand each character's backstory,...

Jiwoo: I really love her character in the webtoon, and I think the adaption here is 80% synchronized. But the Jiwoo in the webtoon is more cold-headed, but there were some parts (e.g her showing her anger, the scene of her cursing) that made me felt disjoined from the character portrated in the webtoon. Also, I honestly would have preferred if there was some development regarding Jiwoo BDSM's tendencies. In the film, her finding out Jihoo's fetish, and coming to accept it all came too fast... and the confession scene felt un-Jiwoo for me. In the webtoon, the confession was more like after she sorted out her boundaries etc. Here was more like an order, and Jihoo just adamantly rejected ..
Jihoo: I actually wanted to see some flashback scenes of why he became a male-sub. It was only briefly explained through voiceover dialogue but I felt that it was an important one. There were quite a build up and explanation in the webtoon. I also wished there was more conflicts of Jihoo with himself? In webtoon, there was the vandalism plot (Hana stalker ex-bf) and Ivan (i think they made him into Lee Han here) which had him in stress over his preferences. There was also Jihoo's ex-bf + blind date in the webtoon that were development scenes for Jihoo to question the boundaries between wanting Jiwoo as his master, girlfriend or both. I think since this is a movie, there wasn't time to build on this, so everything felt rush. But of course, there may be a different perspective for watchers whom had not read the webtoon.
-In the webtoon i really liked Hanna & the cafe owner whom was Jihoo's best friend! Their interaction was so cute!! but i think they integrated Hanna's character into Lee El's character, so :( and they removed Jihoo's best friend, whom i actually really like in the webtoon (HE IS SUPER TSUNDERE)
-Also, the confrontation scene between Jihoo's ex and Jiwoo was actually more interesting in the webtoon.. i can't believe they only just brushed by each other in the film :(
-Also Ivan, was one pivotal character i feel in the webtoon because he actually likes Jiwoo (which makes Jihoo nervous) but then also finds out his secret fetish.. but there wasn't much utilization of his character here other than ousting the two's BDSM voice recording...

Acting
I have nothing to pick on about the acting! For Seohyun i am really seeing her in a new light?? Because let's be frank, i think even some SONES would not have expected her to choose such a production!!! But then she nailed it?? it was completely natural for me :D For Junhyoung, i have no comparisons since its the first time i am watching him act, but i would say he really gave me that puppy vibe HAHHA which i think was what the director was going for :)

Overall, as a fan of the webtoon, i will obviously pick the webtoon over the film. But one good thing of this film is, i really liked how they handled the part on gender discrimination at workplace because this is what actually happens irl??? this also justifies why people like Jihoo wants to hide their preferences. I also preferred the film's ending because i did see sides of Jihoo as a man, and not as a sub to Jiwoo after they established their dating + sub & dom r/s in the film but i didnt see much of it in the webtoon... the webtoon was almost likely an open ending. I would say, it's a good watch still. I am curious of opinions of non-readers to be honest since I think my review was very biased since i kept comparing to the webtoon :|